Don't give you chicks any grit.
They should just be eating the chick started food. The don't need grit to digest that, and the food also has the correct amount of calcium.
They will only need grit when they are older, if the food does not contain it. Most layers pellets contain grit mixed in already. Also if they are allowed to free ranger when older they will find all the grit they need themselves.
I had a bad very upsetting time when my pet parrot died. I had him for many years and someone came to my house and told me I was looking after him wrong and he needed grit to digest food. I was so worried I went out and bought some from the pet shop. My bird seemed to like it and ate at and I thought I was doing a good thing.
Then, a few days later he started to wretch and this lead to him throwing up brown slime. I took him to the vet and he had got a crop infection from eating too much of the grit. He never recovered and I was heart broken as I watched him get worse and finally die about a week later, despite lots of expensive treatment. I will never give any of my cage birds grit again......and they are all healthy and living long lives.